Catheter devices having one or more electrodes at their distal end are commonly used for mapping and ablating tissue, e.g., heart tissue. The electrodes are often ring electrodes which are arrayed along a portion of the distal end of the catheter. Most commonly, each of the electrodes is attached to an conductive wire which passes through the inside of the catheter to a controller and power supply outside the catheter. In many cases each of the electrodes is to be individually controlled. As a result, each electrode must be connected to its own conductive wire.
For such devices to be useful the operator must be able to position the electrodes at the precise location to be ablated or mapped. As can be readily imagined, positioning the electrodes at the desired location often involves moving the tip of the catheter along an tortuous path. For example, a catheter can employ a bi-planar deflection system of the type described in U.S. Pat. No. 5,354,297. Such a catheter can be deflected both laterally and vertically. Lateral deflection and control is achieved using a torqueable wire which is more flexible at the distal end than the proximal end. The proximal end of the wire extends out of the catheter and is attached to a rotatable knob. Rotation of this knob transmits rotational torque to the catheter tip. If the distal end of the catheter is deflected vertically, the application of torque causes the tip to deflect laterally. This control system permits precise positioning of the electrodes at a desired location. However, the positioning of the distal end of the catheter, because of the deflection and torquing involved, can place considerable strain on the connection between the electrode and the conducting wire to which it is attached.
Conventionally, ring electrodes are placed on the distal tip of a flexible catheter as follows. A small aperture is made in the wall of the catheter at the location where the electrode is to be positioned, and an insulated conductive wire is threaded distally through the interior of the catheter. The conductive wire is then threaded through the small aperture. The insulation is removed from a distal portion of the conductive wire, and the exposed conductive wire is soldered to the inside of the ring electrode. The ring electrode is then threaded over the distal end of the catheter and slid along the catheter towards the proximal end of the catheter. Simultaneously, the conductive wire is drawn into the catheter through the small aperture until the ring electrode is located over the small aperture and no portion of the conductive wire is visible outside the catheter. This process may strain the connection between the conductive wire and the ring electrode. Assembling a catheter by this process will take a considerable amount of time.
Moreover, if multiple ring electrodes are to be placed on the distal tip of the catheter, the process is considerably more complex and time consuming. For example, if three ring electrodes--a proximal ring electrode, a middle ring electrode, and a distal ring electrode--are to be placed on the distal tip of a catheter, three conductive wires must be passed through the interior of the catheter. The conductive wire for the proximal ring electrode is threaded through a small aperture in the catheter at the ultimate location of the proximal ring electrode, a conductive wire for the middle ring electrode is threaded through a small aperture in the catheter at the ultimate location of the middle ring electrode, and a conductive wire for the distal ring electrode is threaded through a hole at the ultimate location of the distal ring electrode. The conductive wire for the proximal ring electrode is soldered to the proximal ring electrode. The conductive wires for the middle ring electrode and the distal ring electrode are then threaded through the proximal ring electrode, and the conductive wire for the middle ring electrode is soldered to the middle ring electrode. The conductive wire for the distal ring electrode is threaded through the middle ring electrode and soldered to the distal ring electrode. Once all three ring electrodes are attached to their respective conducting wire, the ring electrodes can be passed over the distal end of the catheter and slid towards the proximal end of the catheter while drawing in the excess lengths of conductive wire until each ring electrode is located over the aperture through which its conductive wire passes and each conductive wire is fully within the catheter. In this process the proximal electrode is, of course, placed on the catheter first followed by the middle electrode and finally the distal electrode. As can be easily imagined, the greater the number of electrodes, the more difficult the assembly procedure becomes.
There are other arrangements for attaching a ring electrode to its conducting wire. For example, U.S. Pat. No. 4,444,195 describes a catheter having a number of ring electrodes each of which is attached to a conducting wire. The catheter has multiple pairs of closely spaced apertures--one pair for each ring electrode. Each conductive wire passes through the interior of the catheter until it reaches the pair of openings for its ring electrode. The conductive wire then passes out of the catheter through one aperture of the pair, loops around the catheter, extends over or under the loop and back into the catheter through the other aperture of the pair. A ring electrode is positioned over each pair of apertures and the electrode is bonded by either a compression fit or the use of conductive epoxy interposed between the tubing and the electrode.